This invention relates to the introduction of a gaseous medium in the form of minute bubbles into a volume of liquid, and especially to a gas diffuser for diffusing a gas into a liquid. More particularly, the invention relates to a device for diffusing a gas such as ozone, into water for purposes of purifying the water.
In the treatment of water, water is normally collected in a large pond, tank, or basin. The particular receptacle generally has a manifold structure near the bottom with a series of gas supply tubes arranged in a suitable array. A number of diffuser heads are located along each supply tube to provide a uniform pattern of gas dispersion throughout the lower portion of the volume of the water that is being treated.
The principal operative component of each diffuser head is a gas permeable element communicating with a gas chamber within the head. Gas under pressure is supplied to all the gas supply tubes causing pressurized gas to fill the diffuser head gas chamber. Consequently, gas is forced through the interstices of the porous diffuser element into the water to form minute bubbles or microbubbles.
The diffuser element or sparger is generally formed of a gas permeable, porous material. Generally speaking, the finer the bubbles that can be diffused into the water the better, so that the surface area of gas exposed to the liquid is optimized.
One problem encountered in connection with the use of a gas such as ozone is the highly corrosive nature of the gas itself. The use of most metals and/or organic plastic components in the diffuser head, eventually results in corrosion damage and failure. However, prior art diffuser assemblies have necessarily required some metal components (such as bolts or other threaded fasteners) and some organic components (such as elastomeric seal rings, etc.) that are susceptible to deterioration.
Because of the corrosive nature of ozone, it has been found that an advantageous material for the diffuser is a porous ceramic. This material is inorganic and not vulnerable to the corrosive effects of either the sewage or of ozone gas. One type of diffuser made from porous ceramic material is described in U.S. Pat. No. 4,046,845. That device essentially comprises two components comprising a relatively dense base portion that may be formed of a PVC plastic material or stainless steel, and a porous ceramic diffuser element in the form of a relatively flat circular plate that seats in an annular groove or rabbet formed in the base member. The base member and the interior surface of the ceramic diffuser element define an interior chamber that is supplied with gas through an inlet tube connected to a gas supply pipe.
In this device, a seal ring formed of organic material, such as an elastomer, is positioned at the joint between the base and the outer edge of the ceramic diffuser plate. A threaded metal fastener extends through a central opening in the ceramic plate and is anchored to the base. The fastener is formed of steel and has an organic seal ring positioned between the fastener head and the upper surface of the ceramic plate.
The advantage of this construction is that the porous ceramic material provides an excellent means for diffusing minute bubbles into the liquid being treated, while at the same time, being formed of material that resists the corrosive effects of the environment including reactive gases that are being diffused. One disadvantage of this construction, however, is that the diffuser assembly includes components that are formed of materials that are vulnerable, over a period of time, to the corrosive effects of the environment it is being used in.
The device of the present invention, however, eliminates the difficulties described above and provides an improved diffuser head assembly of simpler construction that resists the corrosive effects referred to above.